Switched mode power supplies as main parts of telecom and commercial systems often dictate their size and electrical performance as well as reliability and costs. As requirements for the key characteristics power density and efficiency of power converters increase, the demands of these evaluation characteristics increase for inductive components particularly. One approach of increasing the power density and the efficiency is to integrate inductive components. Transformers and inductors can be integrated into a single magnetic structure which than reduces cost, increases power density and power efficiency.
A circuit where integrated magnetics is strongly recommended is the current doubler-rectifier which can be used with different double-ended primary topologies such as forward, two transistors-forward, push-pull, half bridge or full bridge converters. The current-doubler rectifier circuit, habitually applied for low voltage and high current outputs, uses one simple two-winding transformer and two output inductors. The current-doubler rectifier then exhibits lower conduction losses than the conventional center tapped rectifier. This configuration results, additionally to the number of discrete magnetic components which yield higher size and costs, in three high current windings and several high interconnection losses which negatively impact the efficiency.
In U.S. Pat. No. 6,784,644 (Virginia Tech Intellectual Properties Inc.), an integrated magnetic structure for a current-doubler rectifier was introduced, where the transformer secondary winding and secondary inductor windings were integrated, resulting in the removing of the secondary inductor windings with the functionality of the rectifier being guaranteed. Due to introduction of an air gap, the secondary windings not just transform but also store energy. The cores together with the windings integration cause the cost to be reduced and power density to be increased. The reduction of the number of secondary windings and high current interconnections result in lower winding losses. The tight coupling of primary and secondary windings yields minimized leakage inductance.
Another integrated magnetic structure for a current doubler rectifier is disclosed in EP 2 299 456 A1 (DET International Holding Limited). Standardized U/UR cores with bobbinless U/UR cores are used which can be manufactured in high quantities, and therefore manufactured with reduced costs. The tight core-winding coupling yields lower leakage, minimized copper power losses and inductance losses as well as minimized overall thermal resistance. Moreover, the power density increases and the costs are reduced with the absence of bobbins with reduced costs per piece.
The integrated magnetic structures shown in U.S. Pat. No. 6,549,436 (Innovative Technology Licensing LLC), U.S. Pat. No. 6,163,466 (Davila, Jr. et al.), and U.S. Pat. No. 7,034,647 (Northeastern University) comprise four windings: a primary winding, two secondary windings and an additional filter winding which is introduced to further increase the effective inductance and reduce the current ripple in the output of the current-doubler rectifier circuit.
Mostly E cores from retail or sometimes complicated core structures as in U.S. Pat. No. 6,980,077 (ColdWatt, Inc.) are used.
While the described patent addresses some proposed ameliorations, there are still some setbacks. These cores are not flexible in terms of mounting and of adjusting the magnetizing inductance and filtering inductance through the air gap. Also, conventional conductors (round wire and litz) are not adequate for high current secondary windings.